The present invention relates to a method of monitoring the compaction of a fill and in particular of that region of a fill which ensures that a pipe is embedded.
Such a fill must be sufficiently compacted, that is to say have a high enough density to constitute an effective foundation for the pipe, particularly when it is intended to run under a road.
It is known to use a penetrometer for monitoring the compaction of a fill.
Another known technique consists in using a gamma probe and in measuring the absorption of the gamma rays by the fill.
In general, these techniques do not make it possible to obtain a precise indication of the quality of the compaction of a fill, and in particular of the region for embedding a pipe, insofar as, on the one hand, this region is difficult to access and, on the other hand, the quality of the compaction in this region may vary rapidly, in the vertical direction between the raft and the key, and in the horizontal direction, the measurements being taken at discrete points.
The object of the invention is to remedy these drawbacks.
The subject of the invention is therefore a method of monitoring the compaction of a fill for embedding a pipe, comprising the steps consisting in:
applying a force to the fill so as to obtain a resulting deformation of the latter,
measuring the deformation of the fill,
computing the elastic modulus of the fill from the applied force and from the measured deformation,
determining the dry density of the fill from the computed elastic modulus and from the nature of the fill, and
comparing the computed dry density with a dry density value corresponding to an optimum compaction of the fill,
characterized in that the force applied to the fill is applied via the pipe and in that the deformation of the fill is obtained by measuring the deformation of the wall of the pipe.
According to one particular characteristic of the monitoring method according to the invention, the step of applying the force to the fill consists in exerting a radial force on two diametrically opposed regions of the wall of the pipe so as to make its cross section approximately oval.
Advantageously, the step of computing the elastic modulus of the fill comprises the step [sic] consisting in computing the stiffness of the fill, by computation of the ratio of the value of the applied force to the value of the resulting deformation, and in computing the modulus of elasticity of the fill from the computed stiffness.
The subject of the invention is also an apparatus for monitoring the compaction of a fill for embedding a pipe, for the implementation of a monitoring method as defined above, characterized in that it comprises means for applying a force to the wall of the pipe so as to deform it, means for measuring the resulting deformation of the wall of the pipe and a central processing unit to which the said measurement means are connected and comprising means for computing the dry density of the fill from the values of the applied force and from the resulting deformation of the wall of the pipe, and means for comparing the dry density value delivered by the computing means with a dry density value corresponding to an optimum compaction of the fill.
The monitoring apparatus according to the invention may furthermore comprise one or more of the following characteristics, taken separately or according to any technically possible combination:
the means for applying a force to the wall of the pipe comprise at least one cylinder, and the apparatus furthermore comprises a pressure sensor which is placed in the fluid feed circuit for the or each cylinder and is connected to the central processing unit;
it comprises two groups of at least one cylinder, the cylinder or cylinders of one of the groups exerting, in operation, a force in an opposite direction to that exerted by the cylinder or cylinders of the other group;
each group of cylinders comprises a pair of cylinders placed on either side of the means for measuring the deformation of the pipe;
it comprises two blocks for pressing against the internal surface of the wall of the pipe, each block being mounted on the active ends of the cylinders of one of the pairs of cylinders;
each block has two opposed end regions, each provided with means for mounting on a cylinder, and a central region on the external face of which a circular plate for applying the force to the pipe is mounted;
each circular plate and each block are provided with a hole for passage of the means for measuring the deformation of the wall of the pipe;
each circular plate has a disk shape, the diameter of which is approximately equal to one tenth of the diameter of the pipe.